In order to make high data rate interactive services such as video conferencing available to more residential and small business customers, high-speed data communication paths are required. Although fiber optic cable is the preferred transmission media for such high data rate services, it is not readily available in existing communications networks, and the expense of installing fiber optic cable is prohibitive. Current telephone wiring connections, which consist of copper twisted-pair media, are not designed to support the data rates, or bandwidth, required for interactive services. Asymmetric Digital Subscriber Lines (ADSL) technology has been developed to increase the effective bandwidth of existing twisted-pair connections, allowing interactive services to be provided without requiring the installation of new fiber optic cable.
Discrete Multi-Tone (DMT) is a multi-carrier technique that divides the available bandwidth of twisted-pair connections into many subchannels, or bins. The DMT technique has been implemented in ADSL standard T1.413 for use in ADSL systems. In ADSL, DMT is used to generate 250 separate 4.3125 kHz subchannels from 26 kHz to 1.1 MHz for downstream transmission to the end user, and 26 subchannels from 26 kHz to 138 kHz for upstream transmission by the end user.
The rate at which data is to be transmitted is a function of whether or not a device is implemented as an ADSL central office terminal (ATU-C) or an ADSL remote terminal (ATU-R). According to the ADSL standard T1.413, a device used in an ADSL communications system is designated as either an ATU-C or an ATU-R before digital communications are initiated. Therefore, to be used in the ADSL communications system, the device requires system software and hardware which is dedicated to the device being used as either an ATU-C or an ATU-R, but not both. Until configured as an ATU-C or ATU-R, the passing of specific information such as configuration information is not possible. Such dedicated systems decrease the flexibility of the communication system.